1. Field of the Invention
The present invention relates to a head for an ink jet recording apparatus, and more particularly to a head having a thermal energy generating means and a method of fabricating the same.
2. Description of the Prior Art
Among a variety of the conventional recording methods, a so-called liquid jet recording method (ink jet recording method) is an extremely advantageous recording method because this method is a non-impact recording method satisfactorily free from generation of noise at the time of the recording operation, capable of performing the high speed recording operation and recording data on the plain paper without a special fixing treatment. A variety of methods have been suggested and some of them have been commercialized but some of them are under the research performed for putting them into practical use.
The liquid jet recording method is a method in a droplet which is a recording liquid called "ink" is jetted by any of a variety of principles and ink is allowed to adhere to a recording medium such as paper so that recording is performed.
Also, a novel method relating to the liquid jet recording method has been suggested in U.S. Pat. No. 4,723,129. The basic principle of this method is as follows: thermal pulses are, as information signals, given to recording liquid introduced into a working chamber capable of keeping recording liquid; recording liquid communicated to the working chamber is discharged through a liquid discharge opening to jet as a small droplet by the working force generated during a process in which recording liquid generates vapor bubbles; and then the small droplet is allowed to adhere to the recording medium.
The above-mentioned method can be easily adapted to a high density multi-array configuration capable of performing the high speed recording and the color recording operations. Furthermore, since the structure of the apparatus employed is simpler compared with the conventional structure, the overall size of the recording head can be reduced and it is suitable to be mass-produced. In addition, the advantages obtainable from the IC technology and the microelectronic machining technology, which have been significantly advanced in the semiconductor field, can be satisfactorily utilized, so that the overall length can be elongated. As described above, the aforesaid method displays wide applicability.
A typical recording head for a liquid jet recording apparatus adapted to the above-mentioned liquid jet recording method has a thermal energy generating means for forming jetting droplets by discharging recording liquid from the liquid discharge opening.
FIGS. 2 and 3 illustrate the structure of the thermal energy generating means for the conventional recording head, where FIG. 2 is a plan view and FIG. 3 is a cross sectional view taken along line A--A of FIG. 2. Referring to FIG. 3, reference numeral 21 represents a silicon (Si) substrate. The Si substrate 21 has a heat regenerating layer 2 made of SiO.sub.2 for regenerating heat and accomplishing electrical insulation, the heat regenerating layer 2 being formed on the Si substrate 21. The heat regenerating layer 2 is formed by, for example, oxidizing the surface of the Si substrate with heat or it may be layered on the surface of the Si substrate 21 by sputtering or the like. The heat regenerating layer 2 has, on the surface thereof, a heat-generating resistance layer 3 made of HfB.sub.2 or the like by, for example, sputtering to have a predetermined thickness. The heat-generating resistance layer 3 has Al electrodes 14 formed on the surface thereof by sputtering or the like to have a predetermined thickness, and is formed into a predetermined shape by the photolithography technology. The portions of the heat-generating resistance layer 3 positioned between the Al electrodes 14 are exposed to outside. The exposed portions serve as heat generating portions 18 for generating heat due to electricity supplied from the Al electrodes 14. The above-mentioned Al electrodes and the heat generating portions 18 form electro-thermal transducers. Each of the electro-thermal transducers has recessed portions formed due to the gap between the heat generating portions 18 and the Al electrodes 14.
Each of the aforesaid electro-thermal transducers has, on the surface thereof, ink-resisting protection layer 7 in order to protect electric corrosion taking place due to the contact of the above-mentioned elements with ink. The ink-resisting protection layer 7 is usually formed into a two-layer structure as shown in FIG. 3. In this example, the protection layer 7 is composed of a lower layer 8 made of SiO.sub.2 for shielding the heat generating portions 18 from ink, and an upper layer 9 made of Ta serving as a cavitation-resisting layer which withstands the cavitation generated when ink bubbles disappear. If necessary, a layer (omitted from illustration) made of tantalum oxide for improving the strength for adhering Ta placed between the upper and the lower protection layers 8 and 9 may be formed.
FIG. 4 is a cross sectional view which illustrates a junction for connecting the electro-thermal transducers. The electrode 14 and the electric line 4 are connected to each other via a contact hole 5.
However, the conventional structure experiences the following problems because of its structure arranged in such a manner that the Al wiring 4 is formed in a region in which the contact hole has a large stepped portion. (1) In a case where the heat-generating resistance layer or the electrodes and the electric line are formed on the substrate by a high density of, for example, about 400 dpi to 1000 dpi for the purpose of performing precise recording operations with high image quality, the electric lines must be thinned considerably and therefore the stepped portion of the protection layer 8 becomes too large and steeply, resulting in the accuracy in the operation of machining the electric lines and the reliability to deteriorate. Furthermore, the covering facility of the Al wiring in the contact hole is unsatisfactory. What is worse, Al is undesirably formed into polycrystal and therefore, if a high density electric current is passed through it, a phenomenon in which the metal atoms in the wiring move undesirably, that is, electromigration, takes place. The electromigration will cause a void to be generated along the grain boundary of the crystal, a problem of coarse grains to arise, or hillocks or whiskers to be enlarged. As a result, heat is undesirably generated at the electric wire and the electric wire will be welded and broken because the cross sectional area of the electric wire is reduced excessively due to the enlargement of the void. (2) In a case where the contact hole 5 is formed inside an ink chamber 12, the unsatisfactory covering facility will cause the ink and the electric wire to come in contact with each other. As a result, corrosion or an electrolysis takes place.